One of the rear electric windows is not working, i thought it was the door control module, but i changed it, still just clicks, anyway upon checking for earth/wiring and battery faults, my battery reads over 14 volts, with engine off!
Am i right in thinking the battery is shot?

 

That is certainly not a normal voltage. It should be 12.6v with the engine off. Maybe the 14v with the engine running. Not sure how that can happen since battery voltage is sorta built into the physics of lead and acid.

 

So, is it possible the battery has a short

 

The 14V is float voltage.

Turn the car off and check after an hour. It won't be 14V any more.

 

Have you done a hard reboot???

Take the earth terminal off the battery, and hold it on the positve terminal on the battery for 20-30 secs.

This will drain any residual current in the capacitors, so when the battery is re-connected, any stored computer brain fart is cleared.

 

A shorted cell will reduce the battery voltage, proportionally, ie by 1/6. I don't know of any battery fault that can put the voltage up.

There is a phenomenon called surface charge where the battery stays at its charging voltage for a while, after charging. You can eliminate this by waiting overnight, or by drawing sone current. Turning on the headlights for 20s will do it, then wait a couple of minutes, then measure the battery voltage. If its still high, the most likely reason is a bad meter.

 

The alternator could be overcharging the battery, no? Are there any regulators in the car to prevent an overcharge? A 12v battery should easily store 2v over capacity without exploding.

 

I don't believe so. As posted, 14V is a sign of surface charge.

 

The altenator has a built in regulator to charge the battery with ~13.8V. That is it...

 

So if there's no current draw and the battery charges to capacity, wouldn't that be 13.8v? 1/5v overcharge is nothing and irrelevant.

 

Normal operating voltage of the alt is 14-14.4V. What does your voltage across the battery measure when the car is running? If it's much above that then the alt regulator could be bad.

What did the voltage read after you followed Mark's test with turning on headlights?

 

You can't charge a battery past 12.7V. The 13.8V charging voltage will drop to 12.7V when charging stops, with some delay while the surface charge dissipates.

 

Surface charge it is! Bad Fluke meter battery

 

I'm no expert for eletrics, but normally, when everything is turned off, the voltage should be around 12, as the batteries are mads to put out a 11-12v voltage... If you can draw more out, then the battery, so my understanding, is dead or dieing...

 

As other suggested, check where is the voltage when the car is running.

Also, turn ignition on and see how much battery voltage drops. It may-be 14+ without any load, but once loaded - back to normal.

And lastly - check your voltmeter, it just may have +2v or so error..

P.S. I think 14+ is actually a good sign, brand new battery usually maintain higher voltage.

 

11-12V is effectively dead.

You want near 12.6V. (There are tables on the net if you want to see how bad lower voltages mean the battery is.)

Anyone without a meter that can read to within 0.1V get a cheap one off ebay for about $5 (£4).

 

Sorry, you're right... Above 12 is required... Your right there! Thanks for correcting me

 

That was my impression too, as adding a load would drop it below sufficient operating voltage.

 

Yep, such low voltages are a sign that the chemical mix is way past its best so producing much power is tough and drops the volts even further.

 

Is 12.55v good, weak, or bad?